1. Field of the Invention
This invention relates to bonding tool tips with resistance and, more particularly, to bonding tool tips with 500 to 99,999 ohms of resistance for bonding electrical connections.
2. Description of the Prior Art
Integrated circuits are typically attached to a lead frame and individual leads are connected to individual bond pads on the integrated circuit with wire. The wire is fed through a tubular bonding tool tip having a bonding pad at the output end. These tips are commonly called capillary tips. An electrical discharge at the bonding tool tip supplied by a separate EFO (electronic flame off) device melts a bit of the wire thereby forming a bonding ball.
Other bonding tools do not have a center tube, but have a feedhole or other feature for feeding the wire as needed. Some bonding tips have no such wire arrangement as the wire is supplied at the location where the wire is insulated and bonded to a magnetic head and then to a flexible wire circuit. Such is the case in magnetic disk recording devices.
When a bonding tip is on the integrated circuit die side of a wire connection, the wire will form a ball on the end of the wire, as above, before reaching the next die bonding pad. The ball then makes intimate contact with a film formed on the die pad on the integrated circuit. The bonding tip is then moved from the integrated circuit die pad, with gold wire being fed out as the tool is moved, onto the bond pad on the lead frame, and then scrubbed laterally by an ultrasonic transducer. Pressure from the bonding tool tip, the transducer, and capillary action, ‘flows’ the wire onto the bonding pad where molecular bonds produce a reliable electrical and mechanical connection.
Bonding tool tips must be sufficiently hard to prevent deformation under pressure and mechanically durable so that many bonds can be made before replacement. Prior art bonding tool tips are made of aluminum oxide, which is an insulator, but provide the durability to form thousands of bonding connections.
Bonding tool tips should also be electrically designed to produce a reliable electrical contact yet prevent electrostatic discharge damage to the part being bonded. Certain prior art devices have a one-or-more volt emission when the tip makes bonding contact. This could present a problem as a one-volt static discharge could generate a 20 milliamp current to flow, which, in certain instances, could cause the integrated circuit to fail due to this unwanted current.